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Here's why Malaysia Airlines thinks the plane went down in the Indian Ocean

By Kelvin Chan and Justin Pritchard, Associated Press

Posted:
03/25/2014 08:58:14 AM CDT

Updated:
03/25/2014 09:45:49 AM CDT

Crewman on board a plane look at their radar while searching for missing Malaysia Airlines Flight MH370 over the Indian Ocean on Monday, March 24. (Richard Wainwright/AP)

A British communications satellite and classroom physics are helping investigators figure out what happened to Malaysia Airlines Flight 370.

It comes down to some faint signals sent from the plane

An analysis of faint signals sent from Malaysia Airlines Flight 370 to an Inmarsat satellite led officials to conclude the plane crashed in a remote area of the southern Indian Ocean. More precise information about the plane's position when it sent the last signals is helping authorities refine the search being undertaken by planes and ships in seas 1,550 miles southwest of Perth, Australia.

Those faint signals were sent once an hour

Even with other communications shut down, the plane sent an automatic signal — a “ping” or a “handshake” — every hour to an Inmarsat satellite. Flight 370 completed six pings, and the time each took to be sent by the plane and received by the satellite showed the plane's range from the satellite, according to the U.K. Air Accidents Investigation Branch. This initial analysis showed the last ping came from a position along one of two vast arcs north and south from the Malaysian Peninsula.

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How sound waves may have helped pinpoint the plane's final position

Think of a horn being honked in a passing car. To an observer, the sound is high pitched as the car approaches and is lower after the car passes. On approach, each successive sound wave is sent from a slightly closer position to the observer. The sound waves get compressed, resulting in a higher frequency. The opposite happens as the car moves away. It's called the Doppler effect.

The same effect applies to the pings, which would arrive to the satellite at a higher frequency if the plane was moving toward the satellite and decrease in frequency when moving away.

How they calculated it all

For the analysis that led to Monday's conclusion the plane had crashed, Inmarsat studied the satellite communications made while the plane was on the ground at Kuala Lumpur airport and early in its flight. It considered aircraft performance, the satellite's fixed location and other known factors.

By knowing how the Doppler effect would apply to the satellite communications, Inmarsat could calculate the possible positions, direction of travel and speed of the plane. It then compared its predictions to six other Boeing 777 aircraft that flew the same day, and found good agreement, according to Malaysian Defense Minister Hishammuddin Hussein.

By determining the area from which the last signal was sent, then estimating fuel left, it “could give you an approximate area of where the aircraft impacted,” said Joseph Bermudez Jr., chief analytics officer and co-founder of AllSource Analysis, a commercial satellite intelligence firm.

Inmarsat did not respond to repeated requests for comment from The Associated Press.